Existing night vision systems, which include optics, a detector, a display, and power supply, are bulky, because state-of-the-art devices are optimized for resolution and sensitivity, but not size and weight. Three types of night vision technologies are currently deployed. A first one makes use of an image intensifier, which amplifies light 30,000 to 1,000,000 times, usually at the wavelength range of 0.4 to 1 micron. Since moonlight or starlight is usually present at night, a scene can be made visible provided there is enough amplification with high signal-to-noise ratio. The image intensifier includes a photocathode, a single or multiple microchannel plate, and a phosphor screen that emits green light, to which the human eye is most sensitive. Light is absorbed by the photocathode and converted to electrons, which are amplified by the microchannel plate. The electrons are then accelerated to the phosphor screen at high voltage (˜600-900V), resulting in the generation of more light. In a typical night vision system, the image intensifier is sandwiched between the imaging optics and eyepiece, resulting in a bulky tubular structure. The image intensifier can also be coupled directly to a CCD detector by using intermediate optics or a fiber bundle.
A second night vision technology is application of active illumination in near infrared wavelengths (˜0.7 to 1 micron) and detection using a conventional silicon based focal plane array such as a CCD or CMOS. The technique is used extensively indoors. For outdoor applications, the range of view is limited by the intensity and directionality of the illumination source. A third technology is thermal imaging. Objects at ambient temperature emit long wavelength infrared radiation at 7.5 to 15 microns. The radiation can be detected using InSb, InGaAs, HgCdTe, a quantum well infrared photodetector (QWIP), or microbolometer focal plane arrays. In many applications, the thermal image is combined with a visible image acquired using conventional silicon focal plane array to provide a thermal map of an object or scene.